test: add cases for handling tiny deficits in formatting and display (#216)

- Introduced tests to ensure that tiny percent, dollar, and count deficits that round to zero return null.
- Updated the `formatDeficitText` function to return null for these cases, enhancing the accuracy of deficit display in the UI.
- Added a test to verify that the `ProviderCard` component correctly hides deficit text that would round to zero.

(cherry picked from commit f91d3ce)

Author: validatedev

src/components/provider-card.test.tsx

@@ -558,6 +558,35 @@ describe("ProviderCard", () => {
     vi.useRealTimers()
   })
 
+  it("hides tiny positive deficit text that would round to zero", () => {
+    vi.useFakeTimers()
+    const now = new Date("2026-02-02T12:00:00.000Z")
+    vi.setSystemTime(now)
+    render(
+      <ProviderCard
+        name="Pace"
+        displayMode="used"
+        lines={[
+          {
+            type: "progress",
+            label: "Behind",
+            used: 50.3,
+            limit: 100,
+            format: { kind: "percent" },
+            resetsAt: "2026-02-03T00:00:00.000Z",
+            periodDurationMs: 24 * 60 * 60 * 1000,
+          },
+        ]}
+      />
+    )
+    expect(screen.getByLabelText("Will run out")).toBeInTheDocument()
+    expect(screen.getByText(/^Runs out in /)).toBeInTheDocument()
+    expect(screen.queryByText("0% in deficit")).not.toBeInTheDocument()
+    expect(screen.queryByText("0% short")).not.toBeInTheDocument()
+    expect(screen.queryByText(/in deficit/i)).not.toBeInTheDocument()
+    vi.useRealTimers()
+  })
+
   it("keeps status-only tooltip when pace projection is not yet available", () => {
     vi.useFakeTimers()
     const now = new Date("2026-02-02T00:45:00.000Z")

src/lib/pace-tooltip.test.ts

@@ -272,4 +272,29 @@ describe("formatDeficitText", () => {
   it("rounds percent deficit", () => {
     expect(formatDeficitText(4.7, { kind: "percent" }, "used")).toBe("5% in deficit")
   })
+
+  it("returns null for tiny percent deficits that round to zero", () => {
+    expect(formatDeficitText(0.3, { kind: "percent" }, "used")).toBeNull()
+    expect(formatDeficitText(0.3, { kind: "percent" }, "left")).toBeNull()
+  })
+
+  it("returns null for tiny dollar deficits that round to zero", () => {
+    expect(formatDeficitText(0.004, { kind: "dollars" }, "used")).toBeNull()
+  })
+
+  it("returns null for tiny count deficits that round to zero", () => {
+    expect(formatDeficitText(0.004, { kind: "count", suffix: "requests" }, "used")).toBeNull()
+  })
+
+  it("shows the first displayable percent deficit", () => {
+    expect(formatDeficitText(0.5, { kind: "percent" }, "used")).toBe("1% in deficit")
+  })
+
+  it("shows the first displayable dollar deficit", () => {
+    expect(formatDeficitText(0.005, { kind: "dollars" }, "used")).toBe("$0.01 in deficit")
+  })
+
+  it("shows the first displayable count deficit", () => {
+    expect(formatDeficitText(0.005, { kind: "count", suffix: "requests" }, "used")).toBe("0.01 requests in deficit")
+  })
 })

src/lib/pace-tooltip.ts

@@ -104,9 +104,18 @@ export function formatDeficitText(
   deficit: number,
   format: ProgressFormat,
   displayMode: DisplayMode
-): string {
+): string | null {
+  if (!Number.isFinite(deficit) || deficit <= 0) return null
+
   const suffix = displayMode === "left" ? "short" : "in deficit"
-  if (format.kind === "percent") return `${Math.round(deficit)}% ${suffix}`
-  if (format.kind === "dollars") return `$${formatFixedPrecisionNumber(deficit)} ${suffix}`
-  return `${formatCountNumber(deficit)} ${format.suffix} ${suffix}`
+  if (format.kind === "percent") {
+    const roundedPercent = Math.round(deficit)
+    return roundedPercent > 0 ? `${roundedPercent}% ${suffix}` : null
+  }
+
+  const roundedToCents = Math.round(deficit * 100) / 100
+  if (roundedToCents <= 0) return null
+
+  if (format.kind === "dollars") return `$${formatFixedPrecisionNumber(roundedToCents)} ${suffix}`
+  return `${formatCountNumber(roundedToCents)} ${format.suffix} ${suffix}`
 }